Method and system for secure data replication data integrity verification

ABSTRACT

Example embodiments of the present invention relate to a method, a system, and a computer program product for verifying the integrity of replicated virtual machine data. The method includes reading data from a production volume at a production site. A representation of the data may be stored at a replica site with the integrity of the data stored in the replica volume being verified according to the representation of the data.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to U.S. patent application Ser. No.14/102,043 entitled “ENCRYPTED VIRTUAL MACHINES IN A CLOUD” filed onDec. 10, 2013 the teachings of which are hereby incorporated herein byreference in their entirety.

A portion of the disclosure of this patent document may contain commandformats and other computer language listings, all of which are subjectto copyright protection. The copyright owner has no objection to thefacsimile reproduction by anyone of the patent document or the patentdisclosure, as it appears in the Patent and Trademark Office patent fileor records, but otherwise reserves all copyright rights whatsoever.

TECHNICAL FIELD

This application relates to virtual machine replication.

BACKGROUND

Computer data is vital to today's organizations, and a significant partof protection against disasters is focused on data protection. Assolid-state memory has advanced to the point where cost of memory hasbecome a relatively insignificant factor, organizations can afford tooperate with systems that store and process terabytes of data.

Conventional data protection systems include tape backup drives, forstoring organizational production site data on a periodic basis. Suchsystems suffer from several drawbacks. First, they require a systemshutdown during backup, since the data being backed up cannot be usedduring the backup operation. Second, they limit the points in time towhich the production site can recover. For example, if data is backed upon a daily basis, there may be several hours of lost data in the eventof a disaster. Third, the data recovery process itself takes a longtime.

Another conventional data protection system uses data replication, bycreating a copy of the organization's production site data on asecondary backup storage system, and updating the backup with changes.The backup storage system may be situated in the same physical locationas the production storage system, or in a physically remote location.Data replication systems generally operate either at the applicationlevel, at the file system level, at the hypervisor level or at the datablock level.

Current data protection systems try to provide continuous dataprotection, which enable the organization to roll back to any specifiedpoint in time within a recent history. Continuous data protectionsystems aim to satisfy two conflicting objectives, as best as possible;namely, (i) minimize the down time, in which the organization productionsite data is unavailable, during a recovery, and (ii) enable recovery asclose as possible to any specified point in time within a recenthistory.

Continuous data protection typically uses a technology referred to as“journaling,” whereby a log is kept of changes made to the backupstorage. During a recovery, the journal entries serve as successive“undo” information, enabling rollback of the backup storage to previouspoints in time. Journaling was first implemented in database systems,and was later extended to broader data protection.

One challenge to continuous data protection is the ability of a backupsite to keep pace with the data transactions of a production site,without slowing down the production site. The overhead of journalinginherently requires several data transactions at the backup site foreach data transaction at the production site. As such, when datatransactions occur at a high rate at the production site, the backupsite may not be able to finish backing up one data transaction beforethe next production site data transaction occurs. If the production siteis not forced to slow down, then necessarily a backlog of un-logged datatransactions may build up at the backup site. Without being able tosatisfactorily adapt dynamically to changing data transaction rates, acontinuous data protection system chokes and eventually forces theproduction site to shut down.

SUMMARY

Example embodiments of the present invention relate to a method, asystem, and a computer program product for verifying the integrity ofreplicated virtual machine data. The method includes reading data from aproduction volume at a production site. A representation of the data maybe stored at a replica site with the integrity of the data stored in thereplica volume being verified according to the representation of thedata.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects, features, and advantages of embodiments disclosed herein may bebetter understood by referring to the following description inconjunction with the accompanying drawings. The drawings are not meantto limit the scope of the claims included herewith. For clarity, notevery element may be labeled in every Figure. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments, principles, and concepts. Thus, features and advantages ofthe present disclosure will become more apparent from the followingdetailed description of exemplary embodiments thereof taken inconjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of a data protection system according to anexample embodiment of the present invention;

FIG. 2 is a block diagram of a write transaction for a journal accordingto an example embodiment of the present invention;

FIG. 3 is a block diagram of a secure data replication system storingdata according to an example embodiment of the present invention;

FIG. 4 is a block diagram of a secure data replication system verifyingintegrity of data according to an example embodiment of the presentinvention;

FIGS. 5A-5D are flow diagrams illustrating methods for storing andverifying integrity of data according to respective example embodimentsof the present invention;

FIG. 6 is a block diagram of an apparatus according to exampleembodiment of the present invention; and

FIG. 7 is an illustration of computer program code according to anexample embodiment of the present invention.

DETAILED DESCRIPTION

The following definitions are employed throughout the specification andclaims.

BACKUP SITE—a facility where replicated production site data is stored;the backup site may be located in a remote site or at the same locationas the production site;

BLOCK VIRTUALIZATION—may be a layer which take back end storage volumesand, by slicing, concatenating and striping, creates a new set ofvolumes that serve as base volumes or devices in the virtualizationlayer;

CLONE—a clone may be a copy or clone of the image or images, drive ordrives of a first location at a second location;

CONTINUOUS DATA PROTECTION (CDP)—may refer to a full replica of a volumeor a set of volumes along with a journal which allows any point in timeaccess, the CDP copy is at the same site, and may be in the same storagearray as the production volume;

CONTINUOUS REMOTE REPLICATION (CRR)—may refer to a full replica of avolume or a set of volumes along with a journal which allows any pointin time access at a site remote to the production volume and on aseparate storage array;

DATA PROTECTION APPLIANCE (DPA)—a computer or a cluster of computers(i.e., a physical device), or a set of processes (i.e., a virtual deviceor a combination of virtual and physical devices), that serve as a dataprotection appliance, responsible for data protection services includinginter alia data replication of a storage system, and journaling of I/Orequests issued by a host computer to the storage system;

DELTA MARKING STREAM—may mean the tracking of the delta between theproduction and replication site, which may contain the meta data ofchanged locations, the delta marking stream may be kept persistently onthe journal at the production site of the replication, based on thedelta marking data the DPA knows which locations are different betweenthe production and the replica and transfers them to the replica to makeboth sites identical;

DISTRIBUTED MIRROR—may be a mirror of a volume across a distance, eithermetro- or geo-, which is accessible at all sites;

FAIL ALL MODE—may be a mode of a volume in the splitter where all writeand read I/Os intercepted by the splitter are failed to the host, butother SCSI command, like read capacity, are served;

GLOBAL FAIL ALL MODE—may be a mode of a volume in the virtual layerwhere all write and read I/Os to the virtual layer are failed to thehost, but other SCSI commands, like read capacity, are served;

HOST—at least one computer or networks of computers that runs at leastone data processing application that issues I/O requests to one or morestorage systems; a host is an initiator with a SAN;

HOST DEVICE—an internal interface in a host, to a logical storage unit;

IMAGE—a copy of a logical storage unit at a specific point in time;

INITIATOR—a node in a SAN that issues I/O requests;

JOURNAL—a record of write transactions issued to a storage system; usedto maintain a duplicate storage system, and to rollback the duplicatestorage system to a previous point in time;

LOGGED ACCESS—may be an access method provided by the appliance and thesplitter in which the appliance rolls the volumes of the consistencygroup to the point in time the user requested and let the host accessthe volumes in a copy on first write base;

LOGICAL UNIT—a logical entity provided by a storage system for accessingdata from the storage system;

LUN—a logical unit number for identifying a logical unit or one or morevirtual disks or virtual LUNs which may correspond to one or morevirtual machines;

MANAGEMENT AND DEPLOYMENT TOOLS—provide the means to deploy, control,and manage DPAs through virtual environment management tools;

MARKING ON SPLITTER—may be a mode in a splitter where intercepted I/Osare not split to an appliance and the storage, but rather changes (metadata) are tracked in a list and/or a bitmap and I/Os are sentimmediately down the I/O stack;

PHYSICAL STORAGE UNIT—a physical entity, such as a disk or an array ofdisks, for storing data in storage locations that can be accessed byaddress;

PRODUCTION SITE—a facility (i.e., physical or virtual) where one or morehost computers run data processing applications that write data to astorage system and read data from the storage system;

REPLICATION PROTECTION APPLIANCE (RPA)—another name for DPA;

SAN—a storage area network of nodes that send and receive I/O and otherrequests, each node in the network being an initiator or a target, orboth an initiator and a target;

SOURCE SIDE—a transmitter (i.e., physical or virtual) of data within adata replication workflow, during normal operation a production site isthe source side; and during data recovery a backup site is the sourceside;

SNAPSHOT—a Snapshot may refer to differential representations of animage, i.e. the snapshot may have pointers to the original volume, andmay point to log volumes for changed locations. Snapshots may becombined into a snapshot array, which may represent different imagesover a time period;

SPLITTER/PROTECTION AGENT—may be an agent running (i.e., in bothphysical and virtual systems) either on a production host, a switch, ora storage array which can intercept IO and split them to a DPA and tothe storage array, fail IO, redirect IO, or do any other manipulation tothe IO; the splitter may be in the IO stack of a system and may belocated in the hypervisor for virtual machines;

STORAGE MEDIUM—may refer to one or more storage mediums such as a harddrive, a combination of hard drives, flash storage, combinations offlash storage, combinations of hard drives, flash, and other storagedevices, and other types and combinations of computer readable storagemediums including those yet to be conceived; a storage medium may alsorefer both physical and logical storage mediums and may include multiplelevel of virtual to physical mappings and may be or include an image ordisk image;

STORAGE SYSTEM—a SAN entity that provides multiple logical units foraccess by multiple SAN initiators;

TARGET—a node in a SAN that replies to I/O requests;

TARGET SIDE—a receiver (i.e., physical or virtual) of data within a datareplication workflow; during normal operation a back site is the targetside, and during data recovery a production site is the target side;

VASA—vSphere storage Application programming interfaces (APIs) forstorage Awareness;

VIRTUAL ACCESS—may be an access method provided by the appliance and thesplitter in which the appliance exposes a virtual volume from a specificpoint in time to the host, the data for the virtual volume is partiallystored on the remote copy and partially stored on the journal;

VIRTUAL VOLUME—may be a volume which is exposed to a host by avirtualization layer and may span across more than one site;

VMDK—a virtual machine disk file containing disk data in a VMFS (analogto a LUN in a block storage array);

VMFS—a virtual machine file system provide by VMware, Inc. for storing avirtual machine; and

WAN—a wide area network that connects local networks and enables them tocommunicate with one another, such as the Internet.

Description of Embodiments Using a Five State Journaling Process

FIG. 1 is a simplified illustration of a data protection system 100, inaccordance with an embodiment of the present invention. Shown in FIG. 1are two sites; Site I, which is a production site, on the right, andSite II, which is a backup site, on the left. Under normal operation theproduction site is the source side of system 100, and the backup site isthe target side of the system. The backup site is responsible forreplicating production site data. Additionally, the backup site enablesrollback of Site I data to an earlier point in time, which may be usedin the event of data corruption of a disaster, or alternatively in orderto view or to access data from an earlier point in time.

During normal operations, the direction of replicate data flow goes fromsource side to target side. It is possible, however, for a user toreverse the direction of replicate data flow, in which case Site Istarts to behave as a target backup site, and Site II starts to behaveas a source production site. Such change of replication direction isreferred to as a “failover”. A failover may be performed in the event ofa disaster at the production site, or for other reasons. In some dataarchitectures, Site I or Site II behaves as a production site for aportion of stored data, and behaves simultaneously as a backup site foranother portion of stored data. In some data architectures, a portion ofstored data is replicated to a backup site, and another portion is not.

The production site and the backup site may be remote from one another,or they may both be situated at a common site, local to one another.Local data protection has the advantage of minimizing data lag betweentarget and source, and remote data protection has the advantage is beingrobust in the event that a disaster occurs at the source side.

The source and target sides communicate via a wide area network (WAN)128, although other types of networks are also adaptable for use withthe present invention.

In accordance with an embodiment of the present invention, each side ofsystem 100 includes three major components coupled via a storage areanetwork (SAN); namely, (i) a storage system, (ii) a host computer, and(iii) a data protection appliance (DPA). Specifically with reference toFIG. 1, the source side SAN includes a source host computer 104, asource storage system 108, and a source DPA 112. Similarly, the targetside SAN includes a target host computer 116, a target storage system120, and a target DPA 124.

Generally, a SAN includes one or more devices, referred to as “nodes”. Anode in a SAN may be an “initiator” or a “target”, or both. An initiatornode is a device that is able to initiate requests to one or more otherdevices; and a target node is a device that is able to reply torequests, such as SCSI commands, sent by an initiator node. A SAN mayalso include network switches, such as fiber channel switches. Thecommunication links between each host computer and its correspondingstorage system may be any appropriate medium suitable for data transfer,such as fiber communication channel links.

In an embodiment of the present invention, the host communicates withits corresponding storage system using small computer system interface(SCSI) commands.

System 100 includes source storage system 108 and target storage system120. Each storage system includes physical storage units for storingdata, such as disks or arrays of disks. Typically, storage systems 108and 120 are target nodes. In order to enable initiators to send requeststo storage system 108, storage system 108 exposes one or more logicalunits (LU) to which commands are issued. Thus, storage systems 108 and120 are SAN entities that provide multiple logical units for access bymultiple SAN initiators.

Logical units are a logical entity provided by a storage system, foraccessing data stored in the storage system. A logical unit isidentified by a unique logical unit number (LUN). In an embodiment ofthe present invention, storage system 108 exposes a logical unit 136,designated as LU A, and storage system 120 exposes a logical unit 156,designated as LU B.

In an embodiment of the present invention, LU B is used for replicatingLU A. As such, LU B is generated as a copy of LU A. In one embodiment,LU B is configured so that its size is identical to the size of LU A.Thus for LU A, storage system 120 serves as a backup for source sidestorage system 108. Alternatively, as mentioned hereinabove, somelogical units of storage system 120 may be used to back up logical unitsof storage system 108, and other logical units of storage system 120 maybe used for other purposes. Moreover, in certain embodiments of thepresent invention, there is symmetric replication whereby some logicalunits of storage system 108 are used for replicating logical units ofstorage system 120, and other logical units of storage system 120 areused for replicating other logical units of storage system 108.

System 100 includes a source side host computer 104 and a target sidehost computer 116. A host computer may be one computer, or a pluralityof computers, or a network of distributed computers, each computer mayinclude inter alia a conventional CPU, volatile and non-volatile memory,a data bus, an I/O interface, a display interface and a networkinterface. Generally a host computer runs at least one data processingapplication, such as a database application and an e-mail server.

Generally, an operating system of a host computer creates a host devicefor each logical unit exposed by a storage system in the host computerSAN. A host device is a logical entity in a host computer, through whicha host computer may access a logical unit. In an embodiment of thepresent invention, host device 104 identifies LU A and generates acorresponding host device 140, designated as Device A, through which itcan access LU A. Similarly, host computer 116 identifies LU B andgenerates a corresponding device 160, designated as Device B.

In an embodiment of the present invention, in the course of continuousoperation, host computer 104 is a SAN initiator that issues I/O requests(write/read operations) through host device 140 to LU A using, forexample, SCSI commands. Such requests are generally transmitted to LU Awith an address that includes a specific device identifier, an offsetwithin the device, and a data size. Offsets are generally aligned to 512byte blocks. The average size of a write operation issued by hostcomputer 104 may be, for example, 10 kilobytes (KB); i.e., 20 blocks.For an I/O rate of 50 megabytes (MB) per second, this corresponds toapproximately 5,000 write transactions per second.

System 100 includes two data protection appliances, a source side DPA112 and a target side DPA 124. A DPA performs various data protectionservices, such as data replication of a storage system, and journalingof I/O requests issued by a host computer to source side storage systemdata. As explained in detail hereinbelow, when acting as a target sideDPA, a DPA may also enable rollback of data to an earlier point in time,and processing of rolled back data at the target site. Each DPA 112 and124 is a computer that includes inter alia one or more conventional CPUsand internal memory.

For additional safety precaution, each DPA is a cluster of suchcomputers. Use of a cluster ensures that if a DPA computer is down, thenthe DPA functionality switches over to another computer. The DPAcomputers within a DPA cluster communicate with one another using atleast one communication link suitable for data transfer via fiberchannel or IP based protocols, or such other transfer protocol. Onecomputer from the DPA cluster serves as the DPA leader. The DPA clusterleader coordinates between the computers in the cluster, and may alsoperform other tasks that require coordination between the computers,such as load balancing.

In the architecture illustrated in FIG. 1, DPA 112 and DPA 124 arestandalone devices integrated within a SAN. Alternatively, each of DPA112 and DPA 124 may be integrated into storage system 108 and storagesystem 120, respectively, or integrated into host computer 104 and hostcomputer 116, respectively. Both DPAs communicate with their respectivehost computers through communication lines such as fiber channels using,for example, SCSI commands.

In accordance with an embodiment of the present invention, DPAs 112 and124 are configured to act as initiators in the SAN; i.e., they can issueI/O requests using, for example, SCSI commands, to access logical unitson their respective storage systems. DPA 112 and DPA 124 are alsoconfigured with the necessary functionality to act as targets; i.e., toreply to I/O requests, such as SCSI commands, issued by other initiatorsin the SAN, including inter alia their respective host computers 104 and116. Being target nodes, DPA 112 and DPA 124 may dynamically expose orremove one or more logical units.

As described hereinabove, Site I and Site II may each behavesimultaneously as a production site and a backup site for differentlogical units. As such, DPA 112 and DPA 124 may each behave as a sourceDPA for some logical units, and as a target DPA for other logical units,at the same time.

In accordance with an embodiment of the present invention, host computer104 and host computer 116 include protection agents 144 and 164,respectively. Protection agents 144 and 164 intercept SCSI commandsissued by their respective host computers, via host devices to logicalunits that are accessible to the host computers. In accordance with anembodiment of the present invention, a data protection agent may act onan intercepted SCSI commands issued to a logical unit, in one of thefollowing ways:

-   -   Send the SCSI commands to its intended logical unit;    -   Redirect the SCSI command to another logical unit;    -   Split the SCSI command by sending it first to the respective        DPA. After the DPA returns an acknowledgement, send the SCSI        command to its intended logical unit;    -   Fail a SCSI command by returning an error return code; and    -   Delay a SCSI command by not returning an acknowledgement to the        respective host computer.

A protection agent may handle different SCSI commands, differently,according to the type of the command. For example, a SCSI commandinquiring about the size of a certain logical unit may be sent directlyto that logical unit, while a SCSI write command may be split and sentfirst to a DPA associated with the agent. A protection agent may alsochange its behavior for handling SCSI commands, for example as a resultof an instruction received from the DPA.

Specifically, the behavior of a protection agent for a certain hostdevice generally corresponds to the behavior of its associated DPA withrespect to the logical unit of the host device. When a DPA behaves as asource site DPA for a certain logical unit, then during normal course ofoperation, the associated protection agent splits I/O requests issued bya host computer to the host device corresponding to that logical unit.Similarly, when a DPA behaves as a target device for a certain logicalunit, then during normal course of operation, the associated protectionagent fails I/O requests issued by host computer to the host devicecorresponding to that logical unit.

Communication between protection agents and their respective DPAs mayuse any protocol suitable for data transfer within a SAN, such as fiberchannel, or SCSI over fiber channel. The communication may be direct, orvia a logical unit exposed by the DPA. In an embodiment of the presentinvention, protection agents communicate with their respective DPAs bysending SCSI commands over fiber channel.

In an embodiment of the present invention, protection agents 144 and 164are drivers located in their respective host computers 104 and 116.Alternatively, a protection agent may also be located in a fiber channelswitch, or in any other device situated in a data path between a hostcomputer and a storage system.

What follows is a detailed description of system behavior under normalproduction mode, and under recovery mode.

In accordance with an embodiment of the present invention, in productionmode DPA 112 acts as a source site DPA for LU A. Thus, protection agent144 is configured to act as a source side protection agent; i.e., as asplitter for host device A. Specifically, protection agent 144replicates SCSI I/O requests. A replicated SCSI I/O request is sent toDPA 112. After receiving an acknowledgement from DPA 124, protectionagent 144 then sends the SCSI I/O request to LU A. Only after receivinga second acknowledgement from storage system 108 will host computer 104initiate another I/O request.

When DPA 112 receives a replicated SCSI write request from dataprotection agent 144, DPA 112 transmits certain I/O informationcharacterizing the write request, packaged as a “write transaction”,over WAN 128 to DPA 124 on the target side, for journaling and forincorporation within target storage system 120.

DPA 112 may send its write transactions to DPA 124 using a variety ofmodes of transmission, including inter alia (i) a synchronous mode, (ii)an asynchronous mode, and (iii) a snapshot mode. In synchronous mode,DPA 112 sends each write transaction to DPA 124, receives back anacknowledgement from DPA 124, and in turns sends an acknowledgement backto protection agent 144. Protection agent 144 waits until receipt ofsuch acknowledgement before sending the SCSI write request to LU A.

In asynchronous mode, DPA 112 sends an acknowledgement to protectionagent 144 upon receipt of each I/O request, before receiving anacknowledgement back from DPA 124.

In snapshot mode, DPA 112 receives several I/O requests and combinesthem into an aggregate “snapshot” of all write activity performed in themultiple I/O requests, and sends the snapshot to DPA 124, for journalingand for incorporation in target storage system 120. In snapshot mode DPA112 also sends an acknowledgement to protection agent 144 upon receiptof each I/O request, before receiving an acknowledgement back from DPA124.

For the sake of clarity, the ensuing discussion assumes that informationis transmitted at write-by-write granularity.

While in production mode, DPA 124 receives replicated data of LU A fromDPA 112, and performs journaling and writing to storage system 120. Whenapplying write operations to storage system 120, DPA 124 acts as aninitiator, and sends SCSI commands to LU B.

During a recovery mode, DPA 124 undoes the write transactions in thejournal, so as to restore storage system 120 to the state it was at, atan earlier time.

As described hereinabove, in accordance with an embodiment of thepresent invention, LU B is used as a backup of LU A. As such, duringnormal production mode, while data written to LU A by host computer 104is replicated from LU A to LU B, host computer 116 should not be sendingI/O requests to LU B. To prevent such I/O requests from being sent,protection agent 164 acts as a target site protection agent for hostDevice B and fails I/O requests sent from host computer 116 to LU Bthrough host Device B.

In accordance with an embodiment of the present invention, targetstorage system 120 exposes a logical unit 176, referred to as a “journalLU”, for maintaining a history of write transactions made to LU B,referred to as a “journal”. Alternatively, journal LU 176 may be stripedover several logical units, or may reside within all of or a portion ofanother logical unit. DPA 124 includes a journal processor 180 formanaging the journal.

Journal processor 180 functions generally to manage the journal entriesof LU B. Specifically, journal processor 180 (i) enters writetransactions received by DPA 124 from DPA 112 into the journal, bywriting them into the journal LU, (ii) applies the journal transactionsto LU B, and (iii) updates the journal entries in the journal LU withundo information and removes already-applied transactions from thejournal. As described below, with reference to FIGS. 2 and 3A-3D,journal entries include four streams, two of which are written whenwrite transaction are entered into the journal, and two of which arewritten when write transaction are applied and removed from the journal.

FIG. 2 is a simplified illustration of a write transaction 200 for ajournal, in accordance with an embodiment of the present invention. Thejournal may be used to provide an adaptor for access to storage 120 atthe state it was in at any specified point in time. Since the journalcontains the “undo” information necessary to rollback storage system120, data that was stored in specific memory locations at the specifiedpoint in time may be obtained by undoing write transactions thatoccurred subsequent to such point in time.

Write transaction 200 generally includes the following fields:

-   -   one or more identifiers;    -   a time stamp, which is the date & time at which the transaction        was received by source side DPA 112;    -   a write size, which is the size of the data block;    -   a location in journal LU 176 where the data is entered;    -   a location in LU B where the data is to be written; and    -   the data itself.

Write transaction 200 is transmitted from source side DPA 112 to targetside DPA 124. As shown in FIG. 2, DPA 124 records the write transaction200 in four streams. A first stream, referred to as a DO stream,includes new data for writing in LU B. A second stream, referred to asan DO METADATA stream, includes metadata for the write transaction, suchas an identifier, a date & time, a write size, a beginning address in LUB for writing the new data in, and a pointer to the offset in the dostream where the corresponding data is located. Similarly, a thirdstream, referred to as an UNDO stream, includes old data that wasoverwritten in LU B; and a fourth stream, referred to as an UNDOMETADATA, include an identifier, a date & time, a write size, abeginning address in LU B where data was to be overwritten, and apointer to the offset in the undo stream where the corresponding olddata is located.

In practice each of the four streams holds a plurality of writetransaction data. As write transactions are received dynamically bytarget DPA 124, they are recorded at the end of the DO stream and theend of the DO METADATA stream, prior to committing the transaction.During transaction application, when the various write transactions areapplied to LU B, prior to writing the new DO data into addresses withinthe storage system, the older data currently located in such addressesis recorded into the UNDO stream.

By recording old data, a journal entry can be used to “undo” a writetransaction. To undo a transaction, old data is read from the UNDOstream in a reverse order, from the most recent data to the oldest data,for writing into addresses within LU B. Prior to writing the UNDO datainto these addresses, the newer data residing in such addresses isrecorded in the DO stream.

The journal LU is partitioned into segments with a pre-defined size,such as 1 MB segments, with each segment identified by a counter. Thecollection of such segments forms a segment pool for the four journalingstreams described hereinabove. Each such stream is structured as anordered list of segments, into which the stream data is written, andincludes two pointers—a beginning pointer that points to the firstsegment in the list and an end pointer that points to the last segmentin the list.

According to a write direction for each stream, write transaction datais appended to the stream either at the end, for a forward direction, orat the beginning, for a backward direction. As each write transaction isreceived by DPA 124, its size is checked to determine if it can fitwithin available segments. If not, then one or more segments are chosenfrom the segment pool and appended to the stream's ordered list ofsegments.

Thereafter the DO data is written into the DO stream, and the pointer tothe appropriate first or last segment is updated. Freeing of segments inthe ordered list is performed by simply changing the beginning or theend pointer. Freed segments are returned to the segment pool for re-use.

A journal may be made of any number of streams including less than ormore than 5 streams. Often, based on the speed of the journaling andwhether the back-up is synchronous or a synchronous a fewer or greaternumber of streams may be used.

Image Access

Herein, some information is provided for conventional continuous dataprotection systems having journaling and a replication splitter whichmay be used in one or more embodiments is provided. A replication mayset refer to an association created between the source volume and thelocal and/or remote target volumes, and a consistency group contains oneor more replication sets. A snapshot may be the difference between oneconsistent image of stored data and the next. The exact time for closingthe snapshot may determined dynamically depending on replicationpolicies and the journal of the consistency group.

In synchronous replication, each write may be a snapshot. When thesnapshot is distributed to a replica, it may be stored in the journalvolume, so that is it possible to revert to previous images by using thestored snapshots. As noted above, a splitter mirrors may write from anapplication server to LUNs being protected by the data protectionappliance. When a write is requested from the application server it maybe split and sent to the appliance using a host splitter/driver(residing in the I/O stack, below any file system and volume manager,and just above any multipath driver (such as EMC® PowerPath™), throughan intelligent fabric switch, through array-based splitter, such as EMCCLARiiON®.

There may be a number of image access modes. Image access may be used torestore production from the disaster recovery site, and to roll back toa previous state of the data. Image access may be also to temporarilyoperate systems from a replicated copy while maintenance work is carriedout on the production site and to fail over to the replica. When imageaccess is enabled, host applications at the copy site may be able toaccess the replica.

In virtual access, the system may create the image selected in aseparate virtual LUN within the data protection appliance. Whileperformance may be constrained by the appliance, access to thepoint-in-time image may be nearly instantaneous. The image may be usedin the same way as logged access (physical), noting that data changesare temporary and stored in the local journal. Generally, this type ofimage access is chosen because the user may not be sure which image, orpoint in time is needed. The user may access several images to conductforensics and determine which replica is required. Note that in knownsystems, one cannot recover the production site from a virtual imagesince the virtual image is temporary. Generally, when analysis on thevirtual image is completed, the choice is made to disable image access.

If it is determined the image should be maintained, then access may bechanged to logged access using ‘roll to image.’ When disable imageaccess is disabled, the virtual LUN and all writes to it may bediscarded.

In an embodiment of virtual access with roll image in background, thesystem first creates the image in a virtual volume managed by the dataprotection appliance to provide rapid access to the image, the same asin virtual access. Simultaneously in background, the system may roll tothe physical image. Once the system has completed this action, thevirtual volume may be discarded, and the physical volume may take itsplace. At this point, the system continues to function as if loggedimage access was initially selected. The switch from virtual to physicalmay be transparent to the servers and applications and the user may notsee any difference in access. Once this occurs, changes may be read fromthe physical volume instead of being performed by the appliance. Ifimage access is disabled, the writes to the volume while image accesswas enabled may be rolled back (undone). Then distribution to storagemay continue from the accessed image forward.

In some embodiments in physical logged access, the system rolls backward(or forward) to the selected snapshot (point in time). There may be adelay while the successive snapshots are applied to the replica image tocreate the selected image. The length of delay may depend on how far theselected snapshot is from the snapshot currently being distributed tostorage. Once the access is enabled, hosts may read data directly fromthe volume and writes may be handled through the DPA. The host may readthe undo data of the write and the appliance may store the undo data ina logged access journal. During logged access the distribution ofsnapshots from the journal to storage may be paused. When image accessis disabled, writes to the volume while image access was enabled(tracked in the logged access journal) may be rolled back (undone). Thendistribution to storage may continue from the accessed snapshot forward.

Disable image access may mean changes to the replica may be discarded orthrown away. It may not matter what type of access was initiated, thatis, logged or another type, or whether the image chosen was the latestor an image back in time. Disable image access effectively says the workdone at the disaster recovery site is no longer needed.

Delta Marking

A delta marker stream may contain the locations that may be differentbetween the latest I/O data which arrived to the remote side (thecurrent remote site) and the latest I/O data which arrived at the localside. In particular, the delta marking stream may include metadata ofthe differences between the source side and the target side. Forexample, every I/O reaching the data protection appliance for the source112 may be written to the delta marking stream and data is freed fromthe delta marking stream when the data safely arrives at both the sourcevolume of replication 108 and the remote journal 180 (e.g. DO stream).Specifically, during an initialization process no data may be freed fromthe delta marking stream; and only when the initialization process iscompleted and I/O data has arrived to both local storage and the remotejournal data, may be I/O data from the delta marking stream freed. Whenthe source and target are not synchronized, data may not be freed fromthe delta marking stream. The initialization process may start bymerging delta marking streams of the target and the source so that thedelta marking stream includes a list of all different locations betweenlocal and remote sites. For example, a delta marking stream at thetarget might have data too if a user has accessed an image at the targetsite.

The initialization process may create one virtual disk out of all theavailable user volumes. The virtual space may be divided into a selectednumber of portions depending upon the amount of data needed to besynchronized. A list of ‘dirty’ blocks may be read from the delta markerstream that is relevant to the area currently being synchronized toenable creation of a dirty location data structure. The system may beginsynchronizing units of data, where a unit of data is a constant amountof dirty data, e.g., a data that needs to be synchronized.

The dirty location data structure may provide a list of dirty locationuntil the amount of dirty location is equal to the unit size or untilthere is no data left. The system may begin a so-called ping pongprocess to synchronize the data. The process may transfer thedifferences between the production and replica site to the replica.

A discussion of mirroring may be found in U.S. Pat. No. 7,346,805entitled “PROTECTION OF MIRRORED DATA” issued on Mar. 18, 2008, adiscussion of journaling and some techniques associated with journalingmay be found in U.S. Pat. No. 7,516,287 entitled “METHODS AND APPARATUSFOR OPTIMAL JOURNALING FOR CONTINUOUS DATA REPLICATION” issued on Apr.7, 2009, and a discussion of dynamically adding storage for a journalmay be found in U.S. Pat. No. 7,840,536 entitled “METHODS AND APPARATUSFOR DYNAMIC JOURNAL EXPANSION” issued on Nov. 23, 2010, all of which areassigned to EMC Corporation of Hopkinton, Mass. and are herebyincorporated by reference in their entirety.

Secure Data Replication Data Integrity Verification

Encryption of virtual machines for secure replication is described incopending U.S. patent application Ser. No. 14/102,043 entitled“ENCRYPTED VIRTUAL MACHINES IN A CLOUD” filed on Dec. 10, 2013 theteachings of which are hereby incorporated herein by reference in theirentirety.

Conventional solutions for recovering encrypted virtual machines at abackup site involve storing keys at the backup site. Typically, thesesolutions require that the keys exist at the backup site at all times,since the encryption solution is not usually integrated with thereplication solution. Usually a solution will include encrypting thereplication data with a first key, sending the encrypted data to thereplica site, decrypting the encrypted data at the replica site, andthen writing the data at the replica site to a protected storage whichencrypts the data again using a second key. Generally, this introduces avulnerability since the second key to the storage has to be present atthe replica site throughout the replication process, and not only atrecovery times.

Replication to the public cloud has many security challenges, mainlyaround security of the data. For example, traditional methods do notallow data verification with continuous replication. Although sometraditional methods may allow adding checks with the data, thesetraditional methods require additional storage space in the volume forstoring these checks and cause performance and alignment issues. Exampleembodiments of the present invention overcome these and otherdeficiencies by providing a method and a system for verifying theintegrity of replicated virtual machine data to verify that cloud datawas not tampered with.

FIGS. 3 and 4 are block diagrams of a secure data replication system300, 400 for storing and verifying integrity of data according torespective example embodiments of the present invention at respectivetimes. FIGS. 5A-5D are flow diagrams illustrating methods for storingand verifying integrity of data according to respective exampleembodiments of the present invention. FIGS. 3, 4, and 5A-5D may bedescribed in conjunction.

As illustrated in FIGS. 3 and 4, the system 300, 400 includes aproduction site 305-1, 405-1 and a replica site 305-2, 405-2. Theproduction site 305-1, 405-1 may include a hypervisor 310-1, 410-1operating a virtual data protection appliance (VDPA) 320, 420, asplitter 325, 425 operating in the hypervisor kernel 315, 415, and oneor more user virtual machines (VMs) 330, 430. The production site 305-1,405-1 also may include trusted storage (e.g., a production volume) 335,435 for storing user data, and a key manager 340-1, 440-1 for issuing akey 345, 445 to the VDPA 320, 420 for encryption of user data 350. Thereplica site 305-2, 405-2 also may include a hypervisor 310-2, 410-2operating a VDPA 355, 455 and one or more VMs 360, 460 and a key manager340-2, 440-2 for issuing a key (not shown) to the replica site VDPA 355,455. The replica site 305-2, 405-2 also may include a journal 365, 465and storage (e.g., a replica volume) 370, 470 for storing encrypted userdata.

When production site VM 330 is configured for secured replication, areplica VM 360 is generated at replica site 305-2 with the sameconfiguration of VM 330 on the production site 305-1, and a key 345 isgenerated for VM 330. The key 345 is generated by a key manager 340-1.The key 345 may be generated with a unique key ID which may be laterused for retrieving the key 345 from the key manager 340-1. In certainembodiments, Key IDs may be stored at a replication site journal 365,which may be for persistency, and in the memory of VDPA 355. Key IDsalso may be stored at a production site journal (not shown) on trustedstorage 335. Key IDs also may be stored on the production site VDPA 320.The encrypting VDPA 320 also may store a volatile copy of the key 345for encryption. While the embodiment illustrated in FIGS. 3 and 4 showsa single virtual machine on the production site and the replicationsite, in certain embodiments, the production site and replication sitehypervisors may have multiple virtual machines. In some embodiments, thekey manager may likewise store multiple keys corresponding to multiplevirtual machines.

It should be understood that, as described in copending U.S. patentapplication Ser. No. 14/102,043 entitled “ENCRYPTED VIRTUAL MACHINES INA CLOUD” filed on Dec. 10, 2013, the five step journaling processdescribed above may be performed between the production site 305-1 andthe replica site 305-2 for I/O operations being performed at theproduction site 305-1 and the user data is encrypted, thus not allowingthe plain data to arrive to the replica site. The encrypted data 350″may be sent from the production site VDPA 320 to the replica site VDPA355 to the replica site storage 370. However, in such embodiments, theuser cannot know if the image in the cloud was tampered with (i.e., ifsomeone replaced the encrypted data in the replica site 305-2 (e.g., the“cloud”) with other data; thus, if the user tries to recover data, theimage will be corrupt).

As described above, data protection products, such as EMC RecoverPoint®by EMC Corporation of Hopkinton, Mass. may manage a journal. Exampleembodiments of the present invention add integrity verifications in thejournal for the stream of replicated data arriving at the replica site.As will be described in greater detail below, the system may addperiodic hash values for sections of the volume at the production sitein the journal. In other words, every period of time the system may addwithin the journal a hash value of a portion of the production sitestorage, thus allowing the system to verify the portion is indeedcorrect (i.e., if the portion was not touched again since the hash valuewas changed).

In certain embodiments, when a user wants to recover a volume from apoint in time, the system will look for hash values in the journalaround the relevant point in time and, for each hash value which shouldnot have changed, a checking protocol will run to verify that theencrypted data indeed matches the actual data. In other embodiments, forspecial points in time, the system may include a full list of all thehashes (e.g., points in time which are daily application consistentbackup). Therefore, a user recovering for such points in time will haveassurance that the recovered data is identical to the backed up data. Inyet other embodiments, the integrity verification may be a randomtesting that certain blocks did not change, thus giving partialassurance.

As illustrated in FIGS. 3 and 5A, the production site VDPA 320 may readdata (e.g., plain, unencrypted data) from the trusted storage productionvolume 335 at the production site 305-1 (505) and store a representation(e.g., hash) of the plain data 350′ at the replica site 305-2 (510). Itshould be understood that the encrypted user data 350″ may be sent at adifferent time as described above with reference to the five stepjournaling process. As will be described below, the replica site VDPA355 then may later verify the integrity of the encrypted data 350″stored in the storage 370 of the replica site 305-2 (550).

As illustrated in FIGS. 3 and 5B, to store the representation of thedata 350′ at the replica site 305-2 (510), the production site VDPA 320may generate the representation of the data 350′ (i.e., a hash or othersimilar value) (515) and forward the representation of the data 350′ tothe replica site 305-2. The replica site VDPA 355 then may receive therepresentation of the data 350′ and store the representation of the data350′ to the journal 365 (540). It should be understood that, in apreferred embodiment, hashes are performed on chunks of data (e.g., 1MB). In certain embodiments, performing hashes on a per I/O basis duringthe replication process would be problematic as the data would need tobe reread in order to recalculate the hash.

In certain embodiments, as illustrated in FIGS. 3 and 5C, to generatethe representation of the data 350′ (515), the production site VDPA 320may read plain (i.e., unencrypted) data 350 from the trusted storage 335(520) and then generate the representation of the data 350′ as arepresentation of the plain data by performing an operation (e.g., hash)on the plain data (530) to generate the representation of the data 350′.The representation of the data 350′ then may be sent from the productionsite VDPA 320 to the replica site VDPA 355 using the five stepjournaling process described above, with, in certain embodiments, therepresentation of the data 350′ being written to the journal 365 at thereplica site 305-2 (545). It should be understood that, in certainembodiments, the key 345 may be a key that is not sent to the replicasite 305-2 except for failover situations.

In certain embodiments, the production site VDPA 320 may generate therepresentation of the data 350′ on a periodic basis or, in otherembodiments, based on a volume at the production site 305-2. Exampleembodiments of the present invention are equally as applicable to CDP(i.e., hashes calculated periodically) and snapshots (i.e., hashcalculated for a full snapshot). In other embodiments, when a bookmarkis created, a snapshot also may be created on the production sitestorage 335, with a hash for the snapshot being created and sent to thereplica site journal 365. When a user wants to access this point intime, a full hash of the PIT is available for verification.

In other words, example embodiments of the present invention may includean integrity verification engine that runs at the production site 305-1and periodically reads plain data 350 from the production volume 335 andcreates a hash value 350′ of the plain data 350. The hash 350′ then maybe stored in the replica site journal 365 (e.g., periodically, for achunk of data, or for a point in time). Therefore, if someone has accessto the replica site storage 370 (i.e., a vulnerability) but not thereplica site VDPA 355 they will not be able to tamper with the data.

As illustrated in FIGS. 4 and 5D, the replica site VDPA 455 may verifythe integrity of data stored in a replica volume storage 470 (550), suchas prior to allowing access to the replica volume 470. For example, asillustrated in FIG. 5D, if a user requests access to a point in timeimage at the replica site 405-2, the key 445 for accessing the data maybe transferred from the production site 405-1 to the replica site 405-2.The replica site VDPA 455 then may start verifying integrity of theencrypted data 450″ at the replica site (555). In a preferredembodiment, the replica site VDPA 455 looks for a hash of a data portionwhich was not overwritten in the journal 475. The replica site VDPA 455then may read encrypted data 450″ from the replica site storage 470 anddecrypt it according to the key 445 transferred from the production site405-1 to the replica site 405-2. The replica site VDPA 455 then may takea hash of the decrypted data (not shown) and compare it to the hash 450′of the plain data retrieved from the journal 475. If the newlycalculated hash (not shown) does not match the hash 450′ retrieved fromthe journal 475, the encrypted data 450″ may be marked as tampered with.

Example embodiments of the present invention may perform verification atvarious points, including during image access mode, during replication,and when accessing a point in time.

In certain embodiments, the replica site VDPA 455 may verify encrypteddata integrity when in image access mode. For example, the replica siteVDPA 455 may receive a selection of an image at the replica site andexamine one or more representations of data (i.e., hashes) storedpreviously in the journal 475 at the replica site 405-2 for locations inthe volume 470 not overwritten since the representation of data wasgenerated. Therefore, when the user VM 460 accesses an image, the VDPA455 may look for hash values for the portions of data stored previouslyon the journal for the locations that were not overwritten since thehash value was taken. The VDPA 455 then may verify that the data was nottampered with by calculating the hash value for data 450 in theencrypted storage according to the key 445.

In other embodiments, the replica site VDPA 455 may verify encrypteddata integrity while performing replication. In other words, every timethe VDPA 455 reads a hash 450′ from the journal 475, the VDPA 455 mayverify that the hash 450′ corresponds to the encrypted data 450″ on thereplica site storage 470 and that the encrypted data 450″ was nottampered with again by reading the encrypted data 450″ from the replicasite storage 470, decrypting it using the key 445 transferred from theproduction site 405-1 to the replica site 405-2, and calculating a hashof the decrypted data (not shown) and comparing the newly calculatedhash (not shown) to the hash 450′ retrieved from the journal 475.

In yet other embodiments, for a specific point in time, the VDPA 455 mayreceive a selection of a point in time (e.g., from a user) at thereplica site 405-2. The VDPA 455 then may examine the journal 475 at thereplica site 405-2 prior to the point in time for one or morerepresentations of data (e.g., hashes) 450′.

It should be understood that, in certain embodiments, the VDPA 455 mayprovide access to the encrypted data 450 according to the verificationof the integrity of the data by unencrypting the data according to theprivate key (e.g., key 345 of FIG. 3).

FIG. 6 is a block diagram of an example embodiment apparatus 605according to the present invention. The apparatus 605 may be part of asystem 600 and includes memory 610 storing program logic 615, aprocessor 620 for executing a process 625, and a communications I/Ointerface 630, connected via a bus 635.

The methods and apparatus of this invention may take the form, at leastpartially, of program code (i.e., instructions) embodied in tangiblenon-transitory media, such as floppy diskettes, CD-ROMs, hard drives,random access or read only-memory, or any other machine-readable storagemedium. When the program code is loaded into and executed by a machine,such as the computer of FIG. 6, the machine becomes an apparatus forpracticing the invention. When implemented on one or moregeneral-purpose processors, the program code combines with such aprocessor to provide a unique apparatus that operates analogously tospecific logic circuits. As such, a general purpose digital machine canbe transformed into a special purpose digital machine.

FIG. 7 shows program logic 755 embodied on a computer-readable medium760 as shown, and wherein the logic 755 is encoded incomputer-executable code configured for carrying out the methods of thisinvention, thereby forming a computer program product 700.

The logic for carrying out the method may be embodied as part of theaforementioned system, which is useful for carrying out a methoddescribed with reference to embodiments shown. For purposes ofillustrating the present invention, the invention is described asembodied in a specific configuration and using special logicalarrangements, but one skilled in the art will appreciate that the deviceis not limited to the specific configuration but rather only by theclaims included with this specification.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. Accordingly, the present implementations are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalents of the appended claims.

What is claimed is:
 1. A system, comprising: one or more processors; anda non-transitory computer-readable storage medium having computerprogram code encoded thereon that is executable by the one or moreprocessors to perform operations comprising: receiving a hash ofproduction data that resides at a production volume of a productionsite; storing the hash to a replica site journal of a replica site;receiving an encrypted copy of the production data; storing theencrypted copy of the production data in a replica volume at the replicasite; and verifying integrity of the encrypted data stored in thereplica volume by performing operations, at the replica site,comprising: reading out, and decrypting, the encrypted copy of theproduction data; hashing the decrypted production data; comparing thehash of the decrypted production data with the hash stored in thereplica site journal, and either: marking the decrypted production dataas compromised when the hash of the decrypted production data does notmatch the hash stored in the replica site journal; or, providing accessto the decrypted production data at the replica site when the hash ofthe decrypted production data matches the hash stored in the replicasite journal.
 2. The system of claim 1, wherein decrypting the encryptedcopy of the production data stored at the replica site is performedusing a key that was used to encrypt the data at the production site. 3.The system of claim 1, wherein verifying integrity of the encrypted datastored in the replica volume is performed at one of the following times:when the replica site is in an image access mode; while the replica siteis performing replication; or, at a point in time specified by a user.4. The system of claim 1, wherein the production data comprises aportion of a virtual machine (VM).
 5. The system of claim 1, wherein thereplica site is a public cloud site.
 6. The system of claim 1, whereinthe operations further comprise preventing access to the decryptedproduction data at the replica site when the hash of the decryptedproduction data does not match the hash stored in the replica sitejournal.
 7. The system of claim 1, wherein the hashed portion of thedecrypted production data comprises one or more chunks of data.
 8. Thesystem of claim 1, wherein receiving a hash of production data comprisesreceiving a plurality of hashes, each of which corresponds to arespective portion of the production data.
 9. The system of claim 1,wherein the production data comprises a snapshot.
 10. The system ofclaim 1, wherein data integrity verification is performed whilereplication from the production site to the replica site is ongoing.